Wireless transceiver test bed system and method

ABSTRACT

A system and method for testing wireless transceivers in a virtual wireless environment including emulating an RF environment, creating virtual spectrum users having selectable transmission parameters and physical characteristics and evaluating the operation of the wireless transceiver in the virtual wireless environment.

The present application is a continuation of U.S. patent applicationSer. No. 12/787,699 titled Wireless Transceiver Test Bed System andMethod filed May 26, 2010, which is incorporated by reference herein.

The present disclosure relates to the field of functional andperformance testing of wireless transceivers. More specifically, thisdisclosure describes a system and method for testing wirelesstransceivers in the laboratory where the advantages of laboratorytesting are maintained plus many unique attributes of comprehensivefield testing are made possible.

BACKGROUND

In the process of developing, certifying and deploying wirelesstransceivers such as communications devices, it is necessary to testperformance at various points along the way. This testing can be both toassure that the communications system meets its intended purpose andperformance, and to be sure it does not interfere with other wirelessdevices that share the RF spectrum.

The criticality of this testing process is well illustrated by theactivities in the cognitive radio (CR) technology area. Cognitive Radiosare wireless transceivers that sense spectrum usage by primary users(PU), and adapt their transmission to utilize unused and under usedspectrum to communicate. CR technology is not likely to be widelydeployed until the degree of primary user disruption can be accuratelyknown and kept to acceptable levels with acceptable CR performance. CRperformance and interaction with primary users is very difficult tomeasure and model because of many factors including the potential forlarge numbers of participating nodes, breadth of scenarios andenvironments, and adaptation/cognitive nature of the CR nodes.

To create a context for describing the unique attributes of thepresently disclosed test bed, the current state of the art will besummarized. At the two ends of the “test bed spectrum” are full featuredfield tests and software-based modeling.

Full-featured field tests place the wireless transceivers in a fieldscenario containing some representative RF environment where they willbe operated while test data is collected. These sorts of tests are oftenexpensive and complex to orchestrate, and can lack flexibility sincemixes of test transceiver numbers/types/locations, incumbent RF usernumbers/types/locations and RF propagation conditions cannot besystematically varied to collect comprehensive data. FIG. 1schematically depicts a typical field test equipment setup. WirelessTransceiver Units Under Test (UUT) 100 operate in some RF environment110. The RF emissions are subject to the noise, path loss, multipathtransmission and interferers found in the local RF environment. Testinstrumentation 120 is established to measure the performance of the UUTand other PU of the RF environment. In order to accomplish a field testof this variety, the UUT must be physically located in the test RFenvironment, and test instrumentation must be constructed. In order tovary the numbers/types/locations of UUT and PU, physical units must beacquired and placed in the RF environment. In order to vary the RFenvironment, different field venues must be available. Additionally,test instrumentation must be provided and adapted for each UUT/PU/testenvironment scenario where testing is to be accomplished.

Lab-based testing using cable-based interconnection for RF emissions ofUUT and the RF environment is a prior art approach to testing toovercome the challenges of placing and monitoring devices in the fieldenvironment. FIG. 2 depicts a typical lab-based equipment setup. As infield testing, Wireless Transceiver Units Under Test (UUT) 100 areacquired and instrumented with Test Instrumentation 120. Instead of theRF environment being that found in the field, RF test equipment such assignal generators are used to produce Interferers 210, Noise Generators220, and Path Simulators 200 to simulate path loss and multipath in anRF channel. RF Interconnection 230 is accomplished using RF cables suchas coaxial cables. This test set up approach reduces some of thecomplexities of field testing, but introduces new concerns over RFenvironment realism. Further, it still requires the physicalintroduction of new UUT and RF test equipment into the configuration forcomprehensive transceiver configuration and RF environment results.

A variation on RF cable-connected lab testing has become more prevalentand straightforward as wireless transceiver devices have tended towardsdigital waveforms and digital hardware or software implementation. FIG.3a depicts a typical framework for modern wireless communicationsdevices as defined by the prior art OSI model. Here, different functionsin the Wireless Transceiver 100 are allocated to layers in thefunctional stack 300. The physical layer in stack 300 is where thewaveform-related functionality is contained. The physical layer can besegregated into a digital implementation portion 310 and an analogportion 320. Typical functions in the digital portion 310 are waveformgeneration 330 and digital to analog conversion 340. Typical functionsfound in the analog portion 320 are baseband to RF conversion 350. Otherdigital processing functions associated with non-physical layers (2through 7) are contained in the digital data processing block 360. Thefunctions listed (330, 340, 350, 360) are found in the transmit side ofthe transceiver. Equivalent functions are found in the receive side suchas RF to baseband conversion, analog to digital conversion, and waveformprocessing to recover information. Given this decomposition offunctionality, the UUT can be conveniently implemented in an RFcable-interconnected lab test bed as shown in FIG. 3b . With referenceto FIG. 3b , the UUT is shown implemented in three physical entities; anembedded PC 385 to accomplish Layer 2-7 functionality (“digital dataprocessing” from FIG. 3a ), a Universal Software Radio Peripheral (USRP)380 performing the physical layer digital functions (“digital waveformgeneration” and “digital to analog conversion” from FIG. 3a ), and an RFModule, 375 to perform the physical layer analog functions (“baseband toanalog conversion” from FIG. 3a ). FIG. 3b also introduces a PrimaryUser Simulator, 370 as a piece of RF test equipment to simulate theexistence and characteristics of other users sharing the same channel.

Testing using software-based modeling is economical and flexible, butgenerally falls short in incorporating real world effects, especially inthe area of the wireless environment. These shortcomings contribute tothe inability to convincing stake holders of the CR-primary userinteraction. This is especially true given the nature of the primaryusers, many of whom purchased exclusive rights to use the spectrum.Software-based modeling has become more prevalent and straightforward aswireless transceiver devices have tended towards digital waveforms anddigital hardware or software implementation.

As previously described, FIG. 3a depicts a reference framework formodern wireless communications devices as defined by the prior art OSImodel. Here, different functions in the Wireless Transceiver 100 areallocated to layers in the functional stack 300. Many software-basedtest beds with different relevant attributes exist today.

FIG. 3c depicts another prior art test-bed. Computer-based hardwarehosts a software-based test platform 325 to provide a framework for thesoftware model-based transceiver testing application. In FIG. 3c ,multiple UUT 100 are shown with their OSI model stacks 300. Testinstrumentation functionality 120 serving the same general purpose as inprior test bed architectures is also shown. As these UUT generallyadhere to the OSI model, and are digital in nature, they can be“interconnected” to test functionality at different layers in the OSIstack as shown 315. For example, UUT #1 and UUT #n can be interconnectedat the network, data link or digital physical layer for testing.Completeness and field validity of the testing decreases as theinterconnection of the software-modeled UUT moves away from the physicallayer. Two major shortcomings in the software model testing approach canbe gleaned. First, since the test bed is entirely software based, andtherefore digital, the analog RF effects are not taken into account andare not tested. Some test bed architectures may enhance the testing bysimulating effects of the RF channel in the interconnection function315. Including the important RF channel parameters is difficult andresource stressing in most cases. The second shortcoming is that the UUTmodels may be required to operate in non-real time. In other words, theyoperate in accordance with the execution speed of the software model,which are not necessarily the actual physical UUT speeds. This meansthat time related physical parameters such as waveform time ofarrival/frequency of arrival related to distances between nodes, orrendezvous times where two UUT are tuned to the same RF frequency maynot be accurately modeled.

Many lab-based test beds examples exist today that vary from wired RFinterconnections of physical devices to software-model basedsimulations. A sample list includes:

-   -   Georgia Tech University Test Bed—Multiple primary networks        (non-programmable), CRN with flexibility for multiple CR types,        lab-based with unrealistic channel model    -   Virginia Tech Genetic Algorithm Test bed—Wireless link carrying        video as CR, fixed function wireless interferer, lab wireless        environment    -   MIRAI Cognitive Radio Execution Framework (MIRAI-CREF)—a        scalable multi-thread simulation core supporting parallel        execution capable of integrating with real physical devices, but        over a wired network    -   IRIS (Implementing Radio in Software), developed by CTVR (CTVR,        Trinity College, Dublin, Ireland), a suite of software        components that implement various functions of wireless        communications systems. A system for managing the structure and        characteristics of the components and signal chain. 2 GHz OFDM        platform.    -   The Kansas University Agile Radio (KUAR) platform is a low cost,        flexible RF, small form factor SDR implementation that is both        portable and computationally powerful. This platform features a        flexible-architecture RF front-end that can support both wide        transmission bandwidths and a large center frequency range, a        self-contained, small form factor radio unit for portability, a        powerful on-board digital processing engine to support a variety        of cognitive functions and radio operations, and a low cost        build cycle to easily facilitate broad distribution of the radio        units to other researchers within the community. The KUAR        platform was demonstrated at IEEE DySPAN 2007 in Dublin,        Ireland. This demonstration involved an OFDM-based link        operating in the 5 GHz band [2].    -   The Winlab facility at Rutgers is an initiative to develop a        novel cognitive radio hardware prototype for research on        adaptive wireless networks. This is a network-centric cognitive        radio architecture aimed at providing a high performance        networked environment where each node may be required to carry        out high throughput packet forwarding functions between multiple        physical layers. Key design objectives for the cognitive radio        platform include:        -   multi-band operation, fast frequency scanning, and agility;        -   software-defined modem including waveforms such as DSSS/QPSK            and OFDM operating at speeds up to 50 Mbps;        -   packet processor capable of ad-hoc packet routing with            aggregate throughput ˜100 Mbps;        -   spectrum policy processor that implements etiquette            protocols and algorithms for dynamic spectrum sharing.    -   Rockwell Collins—Software Defined Radio Software Communications        Architecture Waveform Development System (SCA WDS). The Rockwell        Collins SDR WDS includes the FlexNet 2 MHz to 2 GHz        multi-channel SDR. The FlexNet Four offers enhanced capacities        to significantly improve the connectivity, mobility,        versatility, interoperability and exchange of information on the        battlefield.    -   University of California, Berkeley—Test bed based on BEE2, a        multi-FPGA emulation engine, fixed or flexible function primary        nodes, flexible function CR nodes, lab-based with unrealistic        wireless channel model, fixed 2.4 GHz RF band (85 MHZ BW)    -   Virginia Tech OSSIE/Tektronix Test Equipment CORTEKS—CR node        based on OSSIE with Tektronix RF test equipment for primary        node(s), lab radio environment    -   Open Access Research Testbed for Next-Generation Wireless        Networks (ORBIT)—an open-access experimental environment to        evaluate protocols and the performance of applications in        real-world settings utilizing a radio-grid emulator that        consists of radio nodes such as 802.11a/b/g and cognitive radio        devices, includes an option for physical radio devices with lab        wireless environment.    -   DARPA XG field testbed—small-scale, rural terrain, spectrum        overlay realization.    -   NSF GENI Program (large Cog radio testbed)    -   NSF ERC program    -   DARPA IAMANET    -   VA Tech ICTAS VT CORNET (based on USRP II connected to an        embedded PC)—30 nodes with some mobility, GNU radio based,        campus test bed only.    -   Carnegie Mellon Radio Test bed—Provides for real-time physical        layer emulation for RF propagation for multiple 802.11 radios        (not CR test bed, no emulation of primary/secondary user        interaction, uses DSP hardware and FPGAs for channel emulation)    -   OMesh Networks—Zigbee based commercial wireless mesh cognitive        networking system. Supports up to 250 kbps data rates for voice,        low-rate video, and data.    -   NTRG Software Radio Test bed—Networks and Telecommunications        Research Group, Trinity College, Dublin, Ireland.

In reviewing the characteristics of these test beds, a set of attributeshas been identified that illustrate shortcomings in comprehensive,realistic and efficient testing. These desirable attributes include:

-   -   Support wide RF bandwidths—assesses the test bed hardware        capability to simulate/operate in both wide-band RF (greater        than approximately several MHz), and supports multiple RF bands        (separated by tens of MHz). This feature is required for testing        the spectrum sensing functionality in a CR to support dynamic        spectrum access (DSA) within a particular band so as to avoid        interference and primary band users.    -   Support networked wireless transceivers—Many prior art test beds        operate with one or a few nodes in “stand-alone” mode, including        CR nodes.    -   Portable Transceivers—In many surveyed test beds, the test bed        contains non-portable equipment such as test-equipment grade        components (signal generators, spectrum analyzers, arbitrary        waveform generators, etc). While this can be sufficient for lab        testing, it is not suitable to be used in a field environment,        which limits the utility of the test bed. A desirable test bed        attribute would be where the UUT could be exercised in the lab        environment with controlled primary/secondary spectrum        conditions and simulated physical motion, and then brought into        real-world conditions of a live RF environment where it can be        exercised and analyzed under less controlled scenarios to        provide irrefutable and necessary demonstrations of performance.    -   Scalable—While in theory any test bed is scalable, in that the        size of the test bed could be made arbitrarily large and        complex. However, many test beds surveyed utilize lab-grade test        equipment or other highly expensive components that make these        systems not realistically scalable. In order to emulate an        arbitrarily large number of PU and UUT, it would not be cost        effective or easily manageable to use tens or hundreds of users        in the form of lab test equipment.    -   MIMO capable (multi-antenna)—MIMO is considered to be one of the        most promising new advances in spectral efficiency seen in        recent communications systems. As such, it is being included as        a base capability in new wireless standards. Therefore, MIMO        capable hardware, supporting multiple phase coherent antennas        for beamforming, spatial multiplexing, and de-multiplexing, and        associated propagation channel models, is a required component        of a comprehensive test bed.    -   Multiple Realistic Wireless Channel Models—Many test beds do not        offer this basic capability. Many test beds utilize either a        simple AWGN channel or have a limited channel simulation or        emulation capability, enabled by either software fading        algorithms or through highly expensive RF fading channel        simulators which offer point to point signal manipulation (such        as Rayleigh fading, multipath, Doppler shift, etc) on only a few        sources.    -   Waveforms Flexibility—Nearly all surveyed test beds offer very        limited scope of testing and are geared to a single specific        application. A full featured test bed should offer to provide a        test capability for an arbitrary number of PU and UUT.    -   Industry Standard Hardware Interfaces—Utilizing non-proprietary        hardware interfaces provides a much more flexible way to test a        multitude of potentially different hardware devices in the same        test bed. If the main functions, low-level signal processing,        and interfaces to the RF are developed around well-defined and        standardized APIs, hardware interfaces, and hardware abstraction        layers, it will be much simpler to break apart the components        and exercise them as either physical or virtual entities in the        test bed. This will also enable a simpler mechanism to        substitute different RF modules with different RF band        capabilities into the test bed.    -   Incorporates Geolocation—None of the surveyed test beds        incorporate the ability to provide precision geolocation of        detected spectrum users, which is considered to be an inherent        weakness in the effort to develop powerful and effective        wireless devices.    -   Realtime/Non-realtime—Many surveyed test beds have focused on a        real-time capability, which can distract from the purpose of the        testing. An approach where both the UUT and the channel are        synchronous, but running in either real time or non-real time,        satisfies the ability to measure performance and more        importantly, one could simulate a huge number of primary and        secondary users, very complex channel effects, etc, without        extensive hardware resources.    -   Faithfully emulate an RF Environment vs. a Propagation Path        based on Range—some laboratory test beds have the ability to        accurately emulate an RF path between UUT based on range, but do        not emulate the path delay or any other features of a realistic        RF environment such as physical environment or other co-spectrum        transmitters or receivers.    -   Allow testing of a variety of RF systems—RF test beds tend to be        oriented towards testing of one variety of RF systems (such as        communications systems) vs. allow testing of sensing RF systems        (such as radars) or navigation systems (such as GPS), or other        types of RF systems.

Based on this sample set and a plethora of other test beds that exist inindustry and academia, a wireless transceiver test bed approach thatproduces broadly applicable realistic results, and yet is scalable,flexible and affordable does not exist.

The present disclosure utilizes emerging technologies and trends in theareas of digital signal processing, wireless device design, widebandnetworks, computer and software architecture/capability andsoftware-based modeling to provide a means to address theseshortcomings. Specific technology innovations include:

-   -   digital signal processing power and available algorithms and        models    -   ability to digitize RF and convert digital signals to RF with        high fidelity    -   emerging software defined radio (SDR) software architectures,        such as SCA (Software Communications Architecture)    -   emerging commercial off-the-shelf digital radio and SDR        components (hardware and software)    -   ever increasing broadband connectivity between distributed sites    -   comprehensive and advanced RF propagation models    -   RF transceiver models being built in software    -   proliferation of radio functionality being digital and        implemented in software with discrete events (bits, bursts,        frames, etc.).    -   standardization of baseband digitized interfaces to SDRs (such        as the VITA-49 Radio Transport Protocol)    -   proliferation of widely available high-speed computer data        interfaces (such as PCI-Express 2.0) for exchanging large        volumes of data between processing elements with low latency and        high throughput

The present disclosure is not limited to wireless devices in theapplication area of communications, but broadly applies to all wirelessdevices and networks including receive only, transmit only and diverseapplications such as sensing, radar, navigation and jamming.

SUMMARY OF DISCLOSURE

The present disclosure is directed to a system and method for testingwireless transceivers in the laboratory where the advantages oflaboratory testing are maintained plus many unique attributes ofcomprehensive field testing are made possible. Laboratory testingapproaches fall into two general categories: those that use RFcable-interconnected UUT and test equipment, and those that performcomputer simulations and rely on software-based UUT and RF environmentmodels. Laboratory testing advantages include simplicity, costeffectiveness, flexibility in number and type of UUT, scalability withrespect to computer resources, and ease of collaboration as networkedcomputers may distribute and share processing and results. Shortcominginclude realism and flexibility of the wireless channel, the potentialinability to model any real time effects (such as if the simulationsoftware cannot run in real time), inability to move UUT to fieldenvironment, and inability to model wideband RF effects.

The present disclosure describes a novel system and new methods to allowlaboratory-based testing to overcome these shortcomings. Theseinnovations apply to both the RF cable-interconnected laboratoryapproach, and the software model-based approach. In both cases, aVirtual Wireless Channel (VWC) function is introduced that flexibly andaccurately allows the wireless channel to be modeled and exercised. TheUUT is interfaced to the VWC using down/up converted digital RF samplesto allow all significant RF channel effects to be modeled includingmultipath and real time radio wave propagation. The modeling of the realtime effects is facilitated by the introduction of executing the test inpiecewise real time or real time capable hardware, and using metadatawhich is communicated between the UUT and VWC. The metadata contains theinformation needed by the test architecture components to reference thedown/up converted digital RF to the true RF spectrum as well as thegeographic lay down of the RF emitters in the defined for the testscenario. This is enabled by time tags for samples being included in themetadata, and controlling delay through the VWC using the sample timetags. The metadata allows the UUT and VWC to operate in a wideband RFsense. The metadata may include time stamp information, locationinformation, or frequency information including center frequency,bandwidth, power and modulation. Primary Users, Secondary Users andother interference (Virtual Spectrum Users (VSU)) can be created andaccurately emulated in the VWC to create the realistic RF environment.The VSU may have selectable transmission parameters and selectablephysical characteristics. For example, transmission parameters mayinclude frequency, bandwidth, power, modulation. Physicalcharacteristics may include location, speed, direction of motion, andantenna parameters including type, elevation gain, azimuth gain, phase,polarization and orientation. The VSU can be selected to be atransmitter only, a transceiver or a transceiver. The VSU can beselected to be a communication device, a sensor such as a radar, anavigation device, or a jammer and can be the same type or differentthan the UUT.

A test instrumentation plane (TIP) may be introduced to orchestrate thepiecewise testing, pass the metadata and collect and reduceinstrumentation data that is collected as part of the testing. Thesenovel features address the shortcoming with respect to a flexible andrealistic wireless channel model, real time parameter modeling, andwideband RF operation.

These attributes distinguish the present disclosure from some of themost recent prior art, such as the Carnegie Mellon Testbed previouslyintroduced. The Carnegie Mellon testbed connects a single UUT type(802.11 nodes) via digitally emulated RF channel model paths. Thetestbed is best characterized as a single purpose (802.11 communicationsnodes) RF path emulator rather than an RF environment emulator. Thereare no provisions for including necessary virtual spectrum users (VSU)or other interference. The path model uses range to estimate path lossconditions, but does not include any time tagging to allow path delay tobe accurately emulated or other metadata important to accurate RFenvironment emulation Further, the Carnegie Mellon testbed lacks theability to use specific geographic location data such as digital terrainand morphology to emulate RF path conditions necessary for accurate RFenvironment emulation in a manner similar to the present disclosure.

In one embodiment of the present disclosure, methods are described whereUUT can be comprehensively tested in the laboratory, and thentransitioned to the field for additional testing. This embodiment takesadvantage of the partitioning of functionality in modern wirelessdevices along analog/digital component lines as well as the availabilityof modular hardware platforms for wireless transceiver hosting. In thisembodiment, the UUT can be tested in the laboratory using the VWC anddown/up converted digital RF approach, and then an antenna and/or analogRF module can be added to the UUT to allow it to function through the RFhardware conversion in the controlled laboratory setting, and finally ina live field environment for further testing.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a simplified block diagram illustrating the components in atypical prior art field-based testing configuration for a wirelesstransceiver.

FIG. 2 is a simplified block diagram illustrating the components in atypical prior art RF interconnected laboratory-based testingconfiguration for a wireless transceiver. FIG. 3a is a simplifieddiagram illustrating the OSI layers in a representative modern wirelesstransceiver and representative functions performed in the digital andanalog portions of the physical layer. FIG. 3b is a simplified blockdiagram illustrating the components in a typical prior art RFinterconnected laboratory-based testing configuration for a distributedfunctionality wireless transceiver.

FIG. 3c is a simplified block diagram illustrating the components in atypical prior art software model-based testing configuration for awireless transceiver.

FIG. 4 is a simplified block diagram illustrating the placement andfunction of a virtual wireless channel in a laboratory-based testingconfiguration for a wireless transceiver in one aspect of the presentdisclosure.

FIG. 5 is an illustration of the concept for testing in contiguous realtime vs. testing in piecewise real time.

FIG. 6 is a simplified flow diagram illustrating the functional flow fora test bed operating in piecewise real time in one aspect of the presentdisclosure.

FIG. 7a is a simplified block diagram illustrating the components in oneaspect of the present disclosure for digital RF interconnectedlaboratory-based testing configuration for a distributed functionalitywireless transceiver.

FIG. 7b is a simplified block diagram illustrating the components in oneaspect of the present disclosure for analog RF interconnectedlaboratory-based testing configuration for a distributed functionalitywireless transceiver.

FIG. 8 is a simplified illustration of how physical UUT and virtual UUTand other emitters can be jointly tested in the laboratory in one aspectof the present disclosure.

FIG. 9 is a simple illustration of the capability to switch fromlaboratory testing using the VWC to field testing with live RF in oneaspect of the present disclosure.

FIG. 10 is a simple illustration of how physical UUT and virtual UUT andother emitters can be jointly tested in the field in one aspect of thepresent disclosure.

DETAILED DESCRIPTION

The present disclosure describes a system and method for testingwireless transceivers in the laboratory where the advantages oflaboratory testing are maintained plus many unique attributes ofcomprehensive field testing are made possible. Two embodiments of thedisclosure will be described to illustrate the system and methodconcepts.

As previously described, two prior art laboratory test bed approachesexist. The first uses a computer hardware and software platform to hosta software model-based test bed application for wireless transceivers asillustrated in FIG. 3c . As described previously, this approach includesas its advantages simplicity, cost effectiveness, flexibility in numberand type of UUT, scalability with respect to computer resources and easeof collaboration as networked computers may distribute and shareprocessing and results. The shortcoming of the approach include realismand flexibility of the wireless channel, the potential inability tomodel any real time effects, inability to move UUT to field environment,inability to model wideband RF effects, and inability to model dynamicUUT movement and the effects it has on signal propagation.

FIG. 4 illustrates one embodiment which addresses certain of theseshortcomings. FIG. 4 adds virtual wireless channel (VWC) 400 and testinstrumentation plane (TIP) and metadata manager 410. The UUT physicallayer digital portion is connected to the VWC via interconnections 420,as is the TIP. The VWC function is to provide a realistic wirelesschannel model including noise, interference, UUT signal path loss andUUT signal multipath transmission. The VWC can be configured with aselectable number of VSU and other interferers to accurately simulatethe RF environment that might be encountered in different parts of theworld. The VSU may have selectable transmission parameters andselectable physical characteristics. For example, transmissionparameters may include frequency, bandwidth, power, modulation. Physicalcharacteristics may include location, speed, direction of motion, andantenna parameters including type, elevation gain, azimuth gain, phase,polarization and orientation. The VSU can be selected to be atransmitter only, a transceiver or a transceiver. The VSU can beselected to be a communication device, a sensor such as a radar, anavigation device, or a jammer and can be the same type or differentthan the UUT. The VWC also allows for selecting transmission parametersand physical characteristics of the physical UUT.

A key feature of the VWC is that it accepts and passes analog RF ordigitized RF to and from the UUT. In this way, the full effects of thewireless channel can be included in the simulation. The TIP 400 acts asa control mechanism to orchestrate the sequencing of the test bedsimulation, and to collect instrumentation data at the RF and other OSIlayers of the UUT. A key part of the TIP is the metadata manager.Metadata is defined as data that must be passed between the VWC and theUUT to allow real time parameters to be modeled and analyzed. As anexample, metadata can include the relative locations of the UUT and VSUin a geographic region. As the simulation progresses, the delaycharacteristics of the multipath and relative time of arrival of thesignals at each node can be accurately modeled.

In one embodiment, in order for the real time aspects of the simulationto be calculated and tracked, where the VWC is unable to sustain thishigh computational requirement, the simulation is managed in piecewisetime vs. non-real time. The concept of piecewise time is illustrated inFIG. 5. The top illustration 500 is a spectrogram and represents thetime aperture over which the simulation will be run with RF spectrum onthe Y axis (i.e. MHz), and time on the X axis (i.e. seconds). Whiteareas in FIG. 5 indicate the presence of RF energy (i.e. signals), andthe dark area is unused spectrum. In the bottom graphic, 510 “real time”is broken up into segments (denoted UUT epochs, 520) separated by VWCepochs. The simulation operates by alternately processing and creatingRF link information that is relayed between the VWC and the UUT. Thetime interval of the UUT epoch is chosen to be small enough that theoperation of the UUT is unaffected by the discrete time operation.

The processing flow on one embodiment is described in FIG. 6. Based onthe initial metadata 600, the VWC prepares a sample set of downlink(D/L) data composed of down converted RF samples (converted to baseband)and metadata 610 and sends 660 to the UUT enabling the UUT 620 tooperate on the data as if it were received at the proper RF and in realtime. The UUT is enabled and receives the data 630 and processes it 640.It creates uplink (U/L) down converted RF samples (baseband samples) andmetadata to be sent to the VWC 650. The VWC receives the U/L samples andmetadata 660, and creates the next set of D/L data. The processcontinues until the time aperture of the real time simulation iscomplete 680.

In another embodiment, the real time aspects of the simulation arepreserved by having the VWC operate in, or near real time. In this case,the VWC epochs as shown in FIG. 5 become very short, or eliminated asthe VWC processing and UUT processing can occur simultaneously. This canbe accomplished either by taking advantage of the anticipated increasesin computational power available over time, or by implementing the VWCin a way which pre-computes much of the data for the simulation andoperates the remaining real time portions in digital hardware that iscapable of maintaining the necessary real time rate. As an example, inone embodiment, the additive digital values of noise and interference tobe used during the simulation are pre-computed then added to UUT RFsamples during the real time operation. Further, pre-computation of theattenuation, and number and delay for multipath components for the UUTRF samples can be performed simplifying the real time operation. Theremaining real time operations could be implemented in any appropriatehigh speed processor, such as high speed workstation CPUs, digitalsignal processors (DSP), Field Programmable Gate Arrays (FPGA's), orgraphics processor units (GPU's) which can be capable of maintaining thenecessary throughput rates.

The present application rectify several of the shortcomings of thecurrent art. First, a realistic and flexible wireless environment modelis added to allow the simulation to accurately model the affects of theRF environment, and vary the environment to perform comprehensivetesting. Second, real time parameters may be simulated and evaluatedincluding UUT and VSU location and motion. The ability to modelrealistic geographic separation, and pre-programmed or random motion ofUUT and VSU host platforms, provides critical functionality towardfield-realistic testing. This feature can allow abstract field scenariosto be modeled, or actual physical field environments at specificlocations on the earth or in space. Widely available digital terraindata including elevation and land use models currently used in manycommercial RF planning tools could be used to provide the informationnecessary to emulate the terrain effects specific to a geographic area,which would be updated in realtime as the UUTs move through a region.The concept of optionally interfacing the VWC to the digital portion ofthe physical layer, using down converted digitized baseband RF samplerepresentation, coupling metadata and processing in a piecewise realtime manor allows real time parameters to be tracked. Third, theenhancements allow wideband RF effects to be modeled. As part of themetadata, the VWC knows where the UUT receiver(s) will be tuned duringthe next UUT time epoch. The VWC can create digital RF data for any partof the spectrum given the RF environment models in its library. Thiscapability is important to the field of cognitive radio to support thetesting of spectrum sensing and dynamic spectrum usage.

The second prior art laboratory test approach involved an RFcable-interconnected UUT/test equipment configuration as was illustratedin FIGS. 2 and 3 b. The advantages of this approach are simplicity, costeffectiveness, flexibility in number and type of UUT, and tight controlover the test configurations, RF environment and collectable results.Shortcoming include realism and flexibility of the wireless channel,inability to model many real time effects, inability to instrumentprocesses internal to the UUT, and limited ability to collaborativelytest.

FIG. 7a illustrates one embodiment of laboratory testing that mitigatesmany of the shortcomings associated with prior art laboratory testing.FIG. 7a illustrates the new architecture based on the prior artarchitecture from FIG. 3b . The analog RF interconnection path 230 ofFIG. 3b can be replaced with a digital RF interconnection 730. ThePrimary User Simulators 370 and Interference Simulator 210 have beenreplaced with the VWC 700. The VWC is capable of the functionality asdescribed previously with respect to FIG. 4. This includes the abilityto simulate and create digital RF signals 720 that includes the affectsof primary users (incumbent users in the RF spectrum), secondary users(other inserted users or other UUT), interference (collectively VSU),fading, multipath, noise and Doppler shifts on signals, path loss andshadowing on signals, and includes the ability to create the datapresuming a geographic distribution of the transceivers. This abilitycan include an abstract relative representation of the UUT and VSUphysical location, or can be based on actual physical locations on theearth where digital terrain and morphology can be used to accurateemulate RF path effects. A Test Instrument Plane (TIP) 740, and userinterface for control and analysis 710 has been added. The TIP 740functionality is similar in nature to that described in FIG. 4.

The functionality described for FIG. 7a using digital RF interconnectscan also be implemented with analog RF interconnects as shown in FIG. 7b. Here, the digital RF interconnection 730 in FIG. 7a is replaced byanalog RF interconnection 750 in FIG. 7b . The VWC would include RFto/from digital converter functionality to accommodate the analog RFinterfacing.

The architecture and functionality shown in FIGS. 7a and 7b can becombined with features of the architecture and functionality in FIG. 4to create a test bed architecture that supports both physical UUTdevices as well as software modeled VSU devices. Referring to FIG. 8, anarchitecture with physical primary nodes 810, software modeled primarynodes (virtual primary nodes) 820, physical UUT (secondary nodes) 830and software modeled secondary nodes (virtual UUT/secondary nodes) 840can be combined in the VWC-TIP architecture to facilitate joint testing.Further, the TIP 870, VWC 850, PN 810, VPN 820, SN 830, and VSN 840elements could be distributed physically in different locations andtesting could be accomplished using broadband connections between theelements since all of the data is digital in nature, and the simulationis controlled using the piecewise time approach with metadata.

Referring to the Digital RF interface, 730 in FIG. 7a , note that thePhysical Layer Digital Function has been disconnected from the PhysicalLayer Analog Function 735 to allow the connection to the VWC. Withreference to FIG. 9, this Physical Layer digital function/analogfunction interface 910 can be configured to support VWC 930 or RF module920 connection through a switch 915. An Application Programmer Interface(API) or equivalent 940 can be defined to allow either connection to bemade.

With the switching and API functionality illustrated in FIG. 9, acombination field and laboratory testing architecture can be constructedas shown in FIG. 10. This architecture departs from FIG. 8 by switchingthe RF data connection in the PN 1010 and SN nodes 1020 from digital RF(from/to the VWC) to analog RF using the RF module as shown in FIG. 7a .In this way, field data and VWC data can be used in conjunction to testdevices. This capability is very powerful in that it creates the abilityto enjoy all of the benefits of laboratory and field testing previouslydefined.

The following descriptions serve to illustrate one embodiment of thepresent disclosure to further describe novelty, functionality andbenefits. The wireless nodes to be made up of inexpensive commerciallyavailable Universal Software Radio Peripheral (USRP,(www.ettus.com))+commercially available high performance general purposeprocessing modules such as the General Micro Systems Nucleus P70xproduct (www.gms4sbc.com). These hardware components allow a softwaredefined radio (SDR) to be constructed for a few thousand dollars. Thewireless nodes can use open source GNU software radio componentsavailable free of charge from a large community of developers. Thewireless nodes would be downloadable with different UUT functionality orwith primary node personalities, to facilitate flexibility in testing.The TIP function serves as an instrumentation layer that can configurethe testing, collect instrumentation data, and provide for post-testdata analysis.

The VWC serves as an abstraction of the wireless environment where thewireless nodes normally communicate. The concept for supplying thislayer is to interface to the USRP's at digital RF. A USRP is made up ofa baseboard with all digital processing (A/D, D/A, gate array, digitalreceivers, digital up converter, digital high speed interfaces, etc.),and daughter cards/RF modules that include all of the RF functions (RFup and down conversion, amplification, switching, local oscillators,etc.). A novel method to create a realistic RF channel is to have theUSRP-based wireless nodes operate without RF daughter cards andinterface with the wireless channel model at digital IF. The functionsin the daughter cards are completely deterministic and straightforward,and can be included in the VWC. From the standpoint of the wirelessnode, it appears to be transmitting and receiving RF, when it isactually sending and receiving digital IF to the VWC. The model caninclude the well known RF channel effects such as path loss, multipath,coherent and non-coherent interference, etc. The connection to thewireless nodes in the VWC can conveniently be made by again using aUSRP, turned “upside down”. They can sink or source digital IF to bebuffered and then operated on by the processing engine that applies theRF channel affects. The USRP has USB2 and gigabit Ethernet (planned) forconvenient interfacing. Interfacing to the VWC can also occur at analogRF by including RF cards with the USRP in both the UUT and the VWC. Oneconsideration in architecting the VWC is the non-real time nature of thefunction (compared to RF propagation time). The approach to overcomethis limitation is to operate the test bed in a piecewise real timemode. As an example of how the piecewise time duration might be chose,consider TDD and framing for the IEEE 802.16 standard, the wirelessnodes will operate in real time for the duration of ½ of a sub-frame(the uplink or downlink portion of a sub-frame), and then wait for theVWC to prepare the next set of RF (digital RF) data to bereceived/transmitted. This approach necessarily requires coordinationwith the wireless nodes, and for the VWC to track and communicate realtime as the test bed operates. These functions will be accomplishedthrough the metadata described previously.

The VWC is realized by operating the radios under test not at the RFlevel, but at the digitized RF level, translated to baseband. Nearly allmodern digital wireless devices/software define radios utilize anarchitecture where on the receive side, the RF is translated to some IF,and then digitized and converted to complex baseband for processing byflash programmable gate arrays (FPGAs), digital signal processors(DSPs), or other general purpose processors. On the transmit side, theopposite process occurs. The VWC will bypass the RF, IF, anddigitization stages of the SDRs under test, and operate directly on thedigital complex baseband data. This eliminates the need to have a veryhigh dynamic range, wide-band RF channel emulation capability, which canbe very costly and complex. Error sources introduced by the RFconversion hardware stage are easily modeled and emulated by the VWC interms of dynamic range impairments, non-linearities, quantization noise,settling times, phase noise, oscillator drift, tuning errors, etc. Theelimination of the RF stage enables the emulated RF channel to exist indigital domain in the form of computer software algorithms residing insomething as simple as a general purpose PC, while giving up real timeoperation of the radios under test. As the channel gets more complex,and if more processing power is required, multiple PCs, or PCs withdedicated computational hardware acceleration could be used to offsetthe demand. Real time operation has no real impact on the performance ofthe radios under test or the environment being simulated. It isenvisioned that both the radios under test and the channel aresynchronous, but potentially running in non-real time. In trying tomanage cost and complexity, the non-real time approach should satisfythe ability to measure performance and more importantly, one couldsimulate a huge number of primary and secondary users, very complexchannel effects, etc, and would not require immense processing power.

The VWC will enable the emulation of literally any RF channel in termsof terrain, multipath, path loss, interference level, andprimary/secondary spectrum users, and geographic separation—somethinglacking in all other prior art test beds. In addition the spectrum userscan be operating in a mode that emulates their true dynamic and adaptivemanner, something not offered by test equipment generating arbitrarywaveforms. For example, even the most sophisticated test equipment thatemulates a wireless cellular link to an actual mobile phone, will notemulate the way in which mobiles are dynamically reassigned spectrum dueto sensed interference from other users. In the VWC, VSUs can be createdand emulated for any device—receive-only, transmit only, other cognitiveusers (secondary users), jammers, radars, etc.

Ideally, most of the components within the UUT will have no knowledge ofthe fact that they are operating against emulated RF signals, versusthose in a real environment. This enables significant work to be done inthe confines of a lab environment before moving to the field, optionallywithout needing the RF portions of the wireless node hardware. Whenmoving to the field, only the RF and RF interface portions are affected,providing a large amount of reusability for all other backend wirelessnode components. The data interface between the signal processingportions and the RF-IF-A/D portions of the device under test will bedefined through a standardized API, utilizing non-proprietarycommunication mechanisms. For example, in the case of the device being aUSRP, the digital base-banded RF would interface to the Virtual WirelessChannel PC through USB 2.0 (480 Mbit/s) or Gigabit Ethernet in the USRP2case. Future devices may utilize higher data rate interfaces such asPCI-Express, or other evolutions of high-speed data interconnectionstandards.

The test instrumentation plane, or TIP, will enable IP-basedcommunication between SDRs or UUT to a control and monitoring computer.The role of the monitoring computer can be to evaluate performance ofall devices under test (and those in the VWC) in response the ongoingVWC activity. In the real world, the devices under test will only haveconnectivity to the outside world over their RF links, which may beeither band-limited, or denied spectrum access due to the currentchannel conditions. The TIP will assist in providing insight into radioperformance in all conditions, in a way that is closely tied andsynchronized to the current activity of all other units under test andto the emulated primary and secondary users. As a result, makingquantifiable assessments of performance in response to certain channelconditions will simply be a matter of querying information from the TIP,which records performance metrics of all devices, and has full knowledgeof the instantaneous spectrum conditions.

It may be emphasized that the above-described embodiments, particularlyany “preferred” embodiments, are merely possible examples ofimplementations, merely set forth for a clear understanding of theprinciples of the disclosure. Many variations and modifications may bemade to the above-described embodiments of the disclosure withoutdeparting substantially from the spirit and principles of thedisclosure. All such modifications and variations are intended to beincluded herein within the scope of this disclosure and the presentdisclosure and protected by the following claims Embodiments of thesubject matter and the functional operations described in thisspecification can be implemented in digital electronic circuitry, or incomputer software, firmware, or hardware, including the structuresdisclosed in this specification and their structural equivalents, or incombinations of one or more of them. Embodiments of the subject matterdescribed in this specification can be implemented as one or morecomputer program products, i.e., one or more modules of computer programinstructions encoded on a tangible program carrier for execution by, orto control the operation of, data processing apparatus. The tangibleprogram carrier can be a propagated signal or a computer readablemedium. The propagated signal is an artificially generated signal, e.g.,a machine-generated electrical, optical, or electromagnetic signal thatis generated to encode information for transmission to suitable receiverapparatus for execution by a computer. The computer readable medium canbe a machine-readable storage device, a machine-readable storagesubstrate, a memory device, or a combination of one or more of them.

The term “circuitry” encompasses all apparatus, devices, and machinesfor processing data, including by way of example a programmableprocessor, a computer, or multiple processors or computers. Thecircuitry can include, in addition to hardware, code that creates anexecution environment for the computer program in question, e.g., codethat constitutes processor firmware, a protocol stack, a databasemanagement system, an operating system, or a combination of one or moreof them.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, or declarative orprocedural languages, and it can be deployed in any form, including as astand alone program or as a module, component, subroutine, or other unitsuitable for use in a computing environment. A computer program does notnecessarily correspond to a file in a file system. A program can bestored in a portion of a file that holds other programs or data (e.g.,one or more scripts stored in a markup language document), in a singlefile dedicated to the program in question, or in multiple coordinatedfiles (e.g., files that store one or more modules, sub programs, orportions of code). A computer program can be deployed to be executed onone computer or on multiple computers that are located at one site ordistributed across multiple sites and interconnected by a communicationnetwork.

The processes and logic flows described in this specification can beperformed by one or more programmable processors executing one or morecomputer programs to perform functions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application specific integrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read only memory ora random access memory or both. The essential elements of a computer area processor for performing instructions and one or more memory devicesfor storing instructions and data. Generally, a computer will alsoinclude, or be operatively coupled to receive data from or transfer datato, or both, one or more mass storage devices for storing data, e.g.,magnetic, magneto optical disks, or optical disks. However, a computerneed not have such devices. Moreover, a computer can be embedded inanother device, e.g., a mobile telephone, a personal digital assistant(PDA), a mobile audio or video player, a game console, a GlobalPositioning System (GPS) receiver, to name just a few.

Computer readable media suitable for storing computer programinstructions and data include all forms of non volatile memory, mediaand memory devices, including by way of example semiconductor memorydevices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks,e.g., internal hard disks or removable disks; magneto optical disks; andCD ROM and DVD-ROM disks. The processor and the memory can besupplemented by, or incorporated in, special purpose logic circuitry.

To provide for interaction with a user, embodiments of the subjectmatter described in this specification can be implemented on a computerhaving a display device, e.g., a CRT (cathode ray tube) or LCD (liquidcrystal display) monitor, for displaying information to the user and akeyboard and a pointing device, e.g., a mouse or a trackball, by whichthe user can provide input to the computer. Other kinds of devices canbe used to provide for interaction with a user as well; for example,input from the user can be received in any form, including acoustic,speech, or tactile input.

Embodiments of the subject matter described in this specification can beimplemented in a computing system that includes a back end component,e.g., as a data server, or that includes a middleware component, e.g.,an application server, or that includes a front end component, e.g., aclient computer having a graphical user interface or a Web browserthrough which a user can interact with an implementation of the subjectmatter described is this specification, or any combination of one ormore such back end, middleware, or front end components. The componentsof the system can be interconnected by any form or medium of digitaldata communication, e.g., a communication network. Examples ofcommunication networks include a local area network (“LAN”) and a widearea network (“WAN”), e.g., the Internet.

The computing system can include clients and servers. A client andserver are generally remote from each other and typically interactthrough a communication network. The relationship of client and serverarises by virtue of computer programs running on the respectivecomputers and having a client-server relationship to each other.

While this specification contains many specifics, these should not beconstrued as limitations on the scope of any invention or of what may beclaimed, but rather as descriptions of features that may be specific toparticular embodiments of particular inventions. Certain features thatare described in this specification in the context of separateembodiments can also be implemented in combination in a singleembodiment. Conversely, various features that are described in thecontext of a single embodiment can also be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination. Similarly, whileoperations are depicted in the drawings in a particular order, thisshould not be understood as requiring that such operations be performedin the particular order shown or in sequential order, or that allillustrated operations be performed, to achieve desirable results. Incertain circumstances, multitasking and parallel processing may beadvantageous. Moreover, the separation of various system components inthe embodiments described above should not be understood as requiringsuch separation in all embodiments, and it should be understood that thedescribed program components and systems can generally be integratedtogether in a single software product or packaged into multiple softwareproducts.

What is claimed is:
 1. A method of processing signals for a wirelessunit under test (UUT) in wireless transceiver test bed having a virtualwireless channel (VWC), comprising the steps: generating a simulationsignal of RF energy; in the VWC, dividing the simulation signal into aplurality of discrete time intervals; processing the simulation signalin piecewise fashion by performing the following steps for each discreteinterval, (i) formatting the RF energy of a first discrete interval ofthe simulation signal to create a first digital baseband signal; (ii)sending the first digital baseband signal to a UUT; (iii) in the UUT,processing the first digital baseband signal and creating a seconddigital baseband signal; (iv) sending the second digital baseband signalto the VWC; (v) in the VWC, processing the second digital basebandsignal for the first discrete time interval received from the UUT toevaluate the behavior of the UUT, and (vi) repeating steps (i) through(vi) for the remaining plurality of discrete intervals of the simulationsignal; wherein the length of the discrete time interval is dependentupon at least one of (a) the processing speed of the VWC and/or the UUT,(b) the processing memory of the VWC and/or the UUT, and (c) thecommunication link between the VWC and the UUT.
 2. The method of claim 1wherein the step of generating a simulation signal of RF energy includesnoise, interference, path loss and multipath transmission.
 3. The methodof claim 1 wherein the step of formatting the RF energy of thesimulation signal to create a first digital baseband signal includespre-computed values for noise and interference.
 4. The method of claim 1wherein the step of formatting the RF energy of the simulation signal tocreate a first digital baseband signal includes pre-computed values forattenuation and the number and delay of multipath components.
 5. Awireless transceiver test bed for testing a wireless unit under test(UUT) comprising: a non-transitory memory for storing computer readablecode; a virtual wireless channel (“VWC”) processor operatively coupledto the memory, the virtual wireless channel processor configured to:generate a simulation signal of RF energy; divide the simulation signalinto a plurality of discrete time intervals; process the simulationsignal in piecewise fashion for each discrete interval, including: (a)format the RF energy of a discrete interval of the simulation signal tocreate a first digital baseband signal; (b) send the first digitalbaseband signal to a UUT; the UUT operatively coupled to the memory, theUUT configured to: (c) process the first digital baseband signal andcreate a second digital baseband signal; (d) send the second digitalbaseband signal to the VWC; and a test processor in the VWC operativelycoupled to the memory, the test processor configured to piecewiseprocess the second digital baseband signals for each of the plurality ofdiscrete time intervals received from the UUT to evaluate the behaviorof the UUT; wherein the length of the discrete time interval isdependent upon at least one of (i) the processing speed of the VWCand/or the UUT, (ii) the processing memory of the of the VWC and/or theUUT, and (iii) the communication link between the VWC and the UUT. 6.The wireless transceiver test bed of claim 5 wherein the virtualwireless channel processor is configured to generate the simulationsignal of RF energy including noise, interference, path loss andmultipath transmission.
 7. The wireless transceiver test bed of claim 5wherein the virtual wireless channel processor is configured to formatthe RF energy of the simulation signal to create a first digitalbaseband signal using pre-computed values for noise and interference. 8.The wireless transceiver test bed of claim 5 wherein the virtualwireless channel processor is configured to format the RF energy of thesimulation signal to create a first digital baseband signal usingpre-computed values for attenuation and the number and delay ofmultipath components.